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Note taking Guide: Mixtures and Solutions

Essential Questions:

1. What’s a solution vs mixture?

2. What’s the difference between a solution, solvent and solute?

3. Can do you quantify concentration?

4. What do some things dissolve while others do not?

5. How can we increase the rate that something dissolves?

Quick: Identify the follow as homogeneous (HO) or heterogeneous (HE) mixtures:

|Milk | |Oil | |

|Muddy water | |Iron | |

|Brass | |Blood | |

|Paint | |Water | |

|Soda | |Sugar water | |

|Flat Soda | |Toothpaste | |

Heterogeneous Mixtures

There are two types of heterogeneous solutions:

• : mixtures containing particles that will settle out if left undisturbed.

o Examples:

• : mixtures of smaller sized particles that do not settle out on their own

o Examples:

Homogeneous Mixtures

• Also called _______________________

• Can be solids, liquids or gases

• phase

• Remain mixed; particles settle out

• Cannot be separated by .

• A solution is formed when a dissolves in a , forming a homogeneous mixture

• Solvent – present in the amount

• Solute – present in the amount

• Solution – Mixture of 2 or more substances that are a mixed homogeneously

Concept Check: Identify the Solvent vs Solute

|Solution |Solvent |Solute |

|Soda | | |

|Lemonade | | |

|Alloys such as brass | | |

|Air | | |

|Antifreeze | | |

|Ocean water | | |

Water

← Water is the most effective .

← Water will dissolve many ionic compounds and most polar covalent compounds

← Water is not effective as a solvent for non-polar covalent compounds

← Effectiveness of water is because water is highly polar with .

Concentration

• The concentration of a solution is usually described as or . .

• There are many ways to express concentration:

Concentration as Percent by Mass

• Ratio of the solutes mass to the mass of the solution expressed as a percentage!

• Amount of solution = ______________________ + _______________________

Let’s try some:

1) What is the percent concentration if 2 grams of sugar is added and dissolved in 10 grams of water?

2) In order to maintain a sodium chloride (NaCl) concentration similar to ocean water, an aquarium must contain 3.6 g NaCl per 100.0 g of water. What is the percent by mass of NaCl in the solution?

Concentration as Molarity

← Another common used by chemist is molarity

← Molarity = the solutions concentration measured as

← Units of M = Moles / Liter

Molarity =

Let’s try some problems:

1) How much sucrose, in moles, is there in 0.5 liters of a 2-molar (2M) solution?

2) To make a 4.0 M solution, how many moles of solute will be needed if 12 L of solution are required?

3) 116.88 grams of NaCl are dissolved in 1.5 liters of solution. What is the molarity of this solution?

Now, try some on your own:

1. What is the percent by mass of 5.0 g of iron (II) sulfate dissolved in 75.0 g of water?

2. A solution is made by adding 25 mL of benzene to 80 mL of toluene. What is the percent by volume of benzene?

3. A solution is formed by adding 35 g of ammonium nitrate to 250 g of water. What is the percent by mass of ammonium nitrate?

4. What is the percent by volume of a solution formed by mixing 25 mL of isopropanol with 45 mL of water?

5. What is the mass percent of each component in the mixture formed by adding 12 g of calcium sulfate, 18 g of sodium nitrate, and 25 g of potassium chloride to 500 g of water?

6. A solution has a volume of 2500 mL. How many liters is this?

7. Convert 50 g of calcium carbonate, CaCO3, into moles.

8. A solution contains 0.42 moles of solute in 0.75 L. Calculate the molarity of the solution.

9. What is the molarity of a solution that contains 15.0 g of NaOH per 500.0 mL of solution?

10. A 250.0 mL solution contains 4.6 g of copper (II) chloride, CuCl2. Find the molarity of this solution.

11. How many moles of hydrochloric acid, HCl, are present in 0.085 L of a 3.0 M solution?

Dilution

What does it mean to dilute a solution?

• In the lab, sometimes reactions call for different strengths or concentration of solutions in order for a reaction to occur.

• We use molarity to create solutions with the proper concentrations.

• Often we need to dilute a stronger solution to a weaker one.

• Solutions can be diluted simply by and leaving the amount of solute unchanged

• What happens to molarity when a solution is diluted?

o More water has been added, so the total volume of solution is greater but the amount of solute is the same

o Molarity will !

• We use the following equation to perform dilution calculations:

M1=Initial molarity; V1= Initial volume; M2= Final molarity; V2=Final volume

Let’s try one! Concentration: percent by mass and molarity, Dilution Demo

1. Calculating percent by mass

• We will be dissolving 2 different amounts of copper chloride in two different 100 mL volumetric flask and then create solutions by adding water.  

• We will use the mass of the solute and mass of the solution to calculate concentration

• Note the colors of the solutions and compare their calculated concentrations

|Solution 1 |Measured |Calculated |

|Mass of empty flask (1) | | |

|Mass of flask with CuCl2 | | |

|Mass of flask with CuCl2 + H2O | | |

|Mass of solute | | |

|Mass of solution | | |

|Concentration for solution 1 | | |

Calculations:

|Solution 2 |Measured |Calculated |

|Mass of empty flask (2) | | |

|Mass of flask with CuCl2 | | |

|Mass of flask with CuCl2 + H2O | | |

|Mass of solute | | |

|Mass of solution | | |

|Concentration for solution 2 | | |

Calculations:

2. Calculating Molarity

• Now, let’s calculate the molarity of each solution

• First, calculate the molar mass of CuCl2

• Then, use the grams and molar mass to calculate moles

• Use moles to calculate Molarity = moles of solute / liters of solutions

|Molarity of Solution 1 |Molarity of Solution 2 |

| | |

| | |

| | |

| | |

| | |

3. Dilution

• Let’s take the mass of a third 100 mL volumetric flask

|Solution 3 |Measured |Calculated |

|Mass of empty flask (3) | | |

|Mass of flask with CuCl2 + H2O | | |

|Mass of solute | | |

|Mass of solution | | |

|Concentration for solution 3 | | |

• Now let’s take 20 mL of the solution one and placed it in the third 100 mL flask

• And then dilute this with water to create a 100mL solution.  

• How many moles of copper chloride are present in that 20 mL?

• What’s the molarity of this new diluted solution?

• What’s the concentration of the new solution?

• How does the molarity, concentration and color compare to solution 2?

Let’s try some problems

1) What would be the resulting molarity of 2.500 L solution when the starting solution had a molarity of 6.00 M and a volume of 417 mL?

2) If I have 340 mL of a 0.5 M NaBr solution, what will the concentration be if I add 560 mL more water to it?

Try some on your own:

12. A stock solution of sodium sulfate, Na2SO4 has a concentration of 1.00 M. The volume of this solution is 50 mL. What volume of a 0.25 M solution could be made from the stock solution?

13. 2.00 mL of a 0.75 M solution of potassium permanganate, K2MnO4 solution is used to make a 500.00 mL solution. What is the concentration of the new solution?

14. A hydrochloric acid solution, HCl has a concentration of 12.1 M. A 41.2 mL sample is used to make a more dilute solution. If the new solution has a concentration of 0.5 M, determine the volume of the solution.

15. A 0.50 M solution of sodium thiosulfate, Na2S2O3 is used to create a more dilute solution. If 250 mL of the concentrated solution is diluted to a volume of 2.5 L, determine the concentration of the new solution.

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Percent by mass =

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